16 research outputs found
Evaluation of the Effect of Chemical or Enzymatic Synthesis Methods on Biodegradability of Polyesters
International audienceThis work compares the biodegradability of polyesters produced by an esterification reaction between glycerol and oleic di-acid (D 18:1) issued from green chemical pathways, via either classical thermo-chemical methods, or an enzymatic method using the immobilized lipase of Candida antartica B (Novozym 435). An elastomeric polymer synthesized by enzymatic catalysis is more biodegradable than an elastomeric thermo-chemical polyester synthesized by a standard chemical procedure. This difference lies in percentage of the dendritic motifs, in values of the degree of substitution, and certainly in cross-links inducing an hyper-branched structure less accessible to the lipolytic enzymes in a waste treatment plant. However, when the elastomeric polymer synthesized by enzymatic catalysis is processed at high temperature as required for certain industrial applications, it presents an identical rate of biodegradation than the chemical polyester. The advantages of the thermo-chemical methods are greater speed and lower cost. Enzymatic synthesis appears be suited to producing polyesters, devoid of metallic catalysts, which must be used without processing at high temperature to keep a high biodegradability
Valuation of bio-based monomers applied to the synthesis of new polyesters
Lâindustrie des matĂ©riaux plastiques, tout comme la majoritĂ© des secteurs dâactivitĂ©, connaĂźt aujourdâhui un nouvel engouement pour les matiĂšres premiĂšres dâorigine renouvelable. Cette tendance sâinscrit dans une dĂ©marche de dĂ©veloppement durable, aspirant Ă la fois Ă trouver des alternatives aux ressources dâorigine fossile, mais aussi Ă concevoir des produits plus respectueux de lâenvironnement. Parmi les composĂ©s issus du monde vĂ©gĂ©tal, il existe non seulement des biopolymĂšres, mais Ă©galement de nombreuses molĂ©cules pouvant ĂȘtre mises Ă profit en tant que monomĂšres. Câest dans ce contexte de valorisation de la biomasse que se positionne ce travail de thĂšse. De nouveaux polyesters bio-sourcĂ©s ont Ă©tĂ© dĂ©veloppĂ©s Ă partir dâun diacide carboxylique dâorigine naturelle : lâacide (Z)-octadĂ©c-9-ĂšnedioĂŻque (D18:1). Cette molĂ©cule est obtenue par oxydation enzymatique de lâextrĂ©mitĂ© alkyle de lâacide olĂ©ique. Afin de mettre en application certains principes de la chimie verte, les polymĂ©risations ont Ă©tĂ© menĂ©es parpolycondensation en masse et catalysĂ©es par des composĂ©s organomĂ©talliques. Divers diols ont Ă©tĂ© polymĂ©risĂ©s avec le D18:1, notamment des diols aliphatiques, aromatiques, phĂ©noliques ou encore certains dianhydrohexitols bio-sourcĂ©s. De plus, la modification chimique du D18:1 a permis de complĂ©ter cette Ă©tude par la synthĂšse de polyesters linĂ©aires entiĂšrement issus de lâacide olĂ©ique. LâĂ©valuation des caractĂ©ristiques physicochimiques des ces nouveaux matĂ©riaux a Ă©tĂ© effectuĂ©e, notamment en termes de masse molaire, de propriĂ©tĂ©s thermiques et rhĂ©ologiques. Des tests prĂ©liminaires de biodĂ©gradation ont permis de dĂ©gager une tendance positive. Cette propriĂ©tĂ© est un atout qui permettrait de substituer certains plastiques issus de la pĂ©trochimie.Nowadays, plastic industry is infatuated with renewable raw materials, as the majority of the business sectors. This trend is in line with the approach of sustainable development, by trying to find alternatives for fossil resources, and by designing more environmentally friendly products. Among compounds coming from vegetable source, there are not only biopolymers, but also numerous molecules which can be used as monomers. This PhD work takes position in this context of biomass valuation. Newbio-based polyesters were developed from a natural carboxylic diacid: the (Z)-octadec-9-enedioic acid(D18:1). This molecule is obtained by enzymatic oxidation of the alkyl end of oleic acid. To apply some green chemistry principles, polymers were synthesized by bulk step-growth polymerization, with organometallic catalysts. Miscellaneous diols were polymerized with D18:1, specifically aliphatic, aromatic and phenolic diols or some bio-based dianhydrohexitols. Furthermore, chemical modifications of D18:1allowed to synthesize linear polyesters entirely based on oleic acid. This new materials were chemically and physically characterized, in terms of molar mass, thermal and rheological properties. The main interest of most of synthesized polyesters is their biodegradability. This advantage could allow these materials to substitute those coming from petrochemistry, in some specific fields of application
Free-surface oscillations control of high speed manipulated liquids
International audienc
Ecrire@LP : collaboration dâenseignants et de chercheurs autour de lâatelier rĂ©dactionnel en lycĂ©e professionnel
International audienc
Linguistique et enseignement du français : recherches au niveau du premier cycle (1969-70 - 1970-71)
Ce recueil est un travail d'Ă©quipe pour une Ă©quipe, un instrument
d'Ă©changes et de communications entre des enseignants
unis par le désir de changer renseignement du français ; et
sans doute, parce qu'il a circulé entre des gens qui se connaissent,
qui se sont unis â ou affrontĂ©s â, qui se sont peu Ă
peu forgé une problématique commune, sans doute parle-t-il
souvent Ă demi-mot, par allusions. Nous aurions pu refaire,
réécrire, polir ; les auteurs de ce livret ont préféré garder une
forme un peu brute. Et, Ă mon sens, ils ont bien fait.
Car ce qui est ici présenté est un texte inscrit dans une pratique,
la pratique de l'enseignant du premier cycle ; ce qui est
mis en cause, c'est un certain modÚle pédagogique ; ce à quoi
nous ne nous résignons pas, c'est à échanger une machine
abstraite imposée contre une autre machine abstraite imposée,
un formalisme contre un autre formalisme, fût-il paré des
plumes des techniques modernes les plus avancées. Pour paraphraser
un récent et remarquable article de Frédéric Gaussen
(Le Monde, 7-8 novembre 1971) : introduire des mathématiques
nouvelles, une linguistique moderne, certes : « mais
qu'y auxa-t-il de profondément modifié si l'enseignement
continue d'ĂȘtre dogmatique ? » Nous voulons que l'enfant manipule,
apprivoise, critique â sans relĂąche â son langage,
celui de ses proches, de la société dans laquelle il vit, découvre,
seul, avec le maĂźtre, avec le mouvement scientifique contemporain,
des hypothÚses de fonctionnement, soit renvoyé aux
faits, aux manipulations et par là , constamment, à la société
qui l'entoure.
Entreprise scandaleuse à beaucoup : l'enseignement du français
Ă©tant depuis son introduction dans l'enseignement (c'est-Ă dire
depuis Port-Royal) extrĂȘmement politisĂ©, lieu privilĂ©giĂ©
de toutes les idéologies, y toucher, c'est toucher à tous les
tabous. Entreprise harassante : la pédagogie ayant été toujours
soigneusement mise à l'écart du Second Degré, à l'Université,
dans les concours, partout, rendue objet de dérision pour plus
de sĂ»retĂ© ; chaque enseignant, nous tous, avons eu tout Ă
apprendre. Mais entreprise passionnante : la théorie des linguistes
se fait modÚle pédagogique, se fait tout autre selon
les milieux, les impératifs sociaux ; elle modifie, elle est
modifiĂ©e ; elle est comme un rĂ©vĂ©lateur et, en mĂȘme temps,
elle instruit. Entreprise enfin qui ne quitte jamais la pratique
d'un pas ; l'enseignant use de la théorie, construit des
modĂšles, analyse, certes ; mais encore plus, il a en charge
soixante enfants qu'il doit suivre jour aprĂšs jour, qu'il doit
faire réussir à des examens souvent absurdes, qu'il doit faire
progresser, comme on dit. Il ne risque pas de se perdre dans
la rĂȘverie.165 page
Novel aliphatic polyesters from an oleic acid based monomer. Synthesis, epoxidation, cross-linking and biodegradation
The synthesis of polymeric materials based on monomers from renewable feedstocks is a steadily growing field. New aliphatic polyesters derived from the 1,18-(Z)-octadec-9-enedioic acid (D18:1), a high oleic sunflower oil fatty acid derivative, and aliphatic diols of different molecular weight (from 1,3-propanediol to 1,12-dodecanediol) have been synthesized and characterized. The polymerization was undertaken by direct bulk polycondensation of a diacid with a diol, with or without a metal catalyst, leading to viscous liquid to solid semi-crystalline polyesters at room temperature, depending on the diol type. The molecular weights of polyesters ranged between 7000 and 20,000 g molâ1. The main attractive aspects of these polyesters are the renewable biomass origin of the diacid and the presence of double bonds on the polymer backbone (oleic acid derivative) allowing subsequent chemical modifications. The epoxidation of these double bonds was undertaken on the macromolecular chains to induce the photochemical cross-linking of the epoxide functions. Transparent and homogeneous cross-linked films were made by photo-polymerization of the epoxy units with less than 5% of extractible products. Enzymatic degradation of these polyesters (cross-linked) was poor over 8 weeks
Synthesis of Linear Polyesters from Monomers Based on 1,18-( Z )-Octadec-9-enedioic Acid and Their Biodegradability
International audienc
Strategies for synthesis of epoxy resins from oleic acid derived from food wastes
The use of biomass-sourced chemical feedstocks creates a conflict over land use between food and fuel/chemical production. Such conflict could be reduced by making use of the annual 1.3 Pg food waste resource. Oleic acid is available from seed oils such as pumpkin, grape, avocado and mango. Its esterification with diols 1,3-propanediol, resorcinol and orcinol was used to form diesters and the naturally occurring norspermidine was used to prepare a diamide, all under ambient conditions. These compounds were then epoxidized and polymerized. When esterification was followed by epoxidation and subsequent curing at elevated temperature with p-phenylenediamine or diethylenetriamine, hard insoluble resins were formed. When the sequence was changed such that the epoxidized oleic acid was first reacted with cis-1,2-cyclohexanedicarboxylic anhydride and then esterified with orcinol and resorcinol, insoluble crosslinked polymers were also obtained
Evaluation of the Effect of Chemical or Enzymatic Synthesis Methods on Biodegradability of Polyesters
Chemical Sensors Based on New Polyamides Biobased on (Z) Octadec-9-Enedioic Acid and ÎČ-Cyclodextrin
International audienceThe synthesis of new biobased polyamides from different ÎČ-cyclodextrin monomers and the (Z) octadec-9-enedioic acid is investigated. The aim of this study is to design different sensors, having different sensibilities and selectivities to a set of various volatile organic compounds (VOC) relevant in the early detection of lung cancer. The sensors are obtained from the synthesized polyamides, using multiwalled carbon nanotubes as conductive nanofillers and a layer by layer process. The conductive polymer nanocomposites (CPC) designed from the heptakis-6-amino ÎČ-cyclodextrin and 6A,6D diamino ÎČ-cyclodextrin have a high affinity for polar protic solvents, while the CPC having a matrix based on 6A,6D diamino 2A-G,3A-G,6B,6C,6E,6F,6G nonadeca-O-benzyl-ÎČ-cyclodextrin develops hydrophobic interactions with nonpolar solvents. Due to a higher accessibility of cyclodextrin, the chemoresistive response of the hydrophilic linear polyamide CPC is larger than one of the hydrophilic branched polyamide CPC. As required, the VOC diffusion/desorption phenomenon is reversible for all the sensors